The present invention generally relates to refrigeration systems and, more particularly, to refrigeration systems having flow-control restriction or expansion devices incorporated therein.
A refrigeration system, such as a motor vehicle air conditioner, typically has a closed circuit through which a refrigerant undergoes a thermodynamic cycle. The circuit of a motor vehicle air conditioner typically includes an engine driven semi-hermetic compressor, a condenser connected in series to the compressor, a flow-control restriction or expansion device, which is typically a fixed orifice tube, connected in series to the condenser, an evaporator connected in series with the expansion device, and an accumulator located in series between the evaporator and the compressor. The compressor raises the pressure of xe2x80x9clow-pressurexe2x80x9d gaseous refrigerant to a pressure suitable for operation of the condenser. xe2x80x9cHigh-pressure hotxe2x80x9d gaseous refrigerant passes from the compressor to the condenser. The condenser condenses the high-pressure hot refrigerant by transferring heat from the refrigerant to the ambient environment or atmosphere located outside the motor vehicle. The expansion device causes the high-pressure liquid refrigerant exiting the condenser to experience a sudden pressure drop, causing the liquid refrigerant to cool and expand (usually a constant enthalpy process). The xe2x80x9clow-pressure coldxe2x80x9d liquid refrigerant passes to the evaporator where it vaporizes by absorbing heat from surrounding air and as a result cools the surrounding air. Typically, a fan or blower forces air across the evaporator and delivers xe2x80x9ccooledxe2x80x9d air to a passenger compartment of the motor vehicle. Low-pressure hot gaseous refrigerant exits the evaporator and returns to the compressor and the above-described thermodynamic cycle repeats as the refrigerant flows through the circuit. The accumulator collects any liquid refrigerant which exits the evaporator.
Such motor vehicle air conditioning systems can be tailored for efficient cooling at specific driving conditions such as, for example, highway driving (constant speed) or city driving (stop and go). The restriction or orifice of the expansion device is typically sized to obtain optimum refrigerant flow for the highway driving. As a result, cooling efficiency under city driving conditions is often less than desirable.
City driving conditions require frequent starts and stops. When the motor vehicle has a fast start or drive away, the compressor speed rapidly increases and can result in a spike in the head pressure of the refrigeration system. This is particularly true with refrigeration systems utilizing xe2x80x9chigh efficiencyxe2x80x9d scroll compressors. These pressure spikes can be very detrimental to the life span of various system components. These pressure spikes can also be high enough to trip a protective cut-off switch of the refrigeration system which is designed to prevent failure of system components such as refrigerant lines or fittings under high pressure. When the cut-off switch is tripped, the compressor is declutched and the refrigeration system is temporarily shut down until the compressor is reconnected. The refrigeration system can be shut down for about 8 seconds or more for each pressure spike. These undesired shut downs of the refrigeration system can dramatically effect cooling efficiency.
To reduce these pressure spikes, and the resulting shut downs of the refrigeration system, the size of the expansion device orifice is often increased to obtain a higher refrigerant flow rate. This increased refrigerant flow rate reduces the pressure spikes and system shut downs. However, the increased flow rate is less than optimum under other driving conditions and results in a drop in cooling efficiency. Accordingly, there is a need in the art for an improved refrigeration system and/or expansion device which reduces head pressure spikes to reduce system shut downs without significantly reducing overall cooling efficiency.
The present invention provides a refrigerant flow-control device operable between a normal low-flow condition and a pressure-relief high-flow condition which overcomes at least some of the above-noted problems related to the prior art. According to the present invention, the refrigerant flow-control device includes a body having an inlet and an outlet and forming a refrigerant passageway extending from the inlet to said outlet and a poppet within said body. The refrigerant passageway having a valve flow passage and first and second restrictions. The poppet is movable between a first position closing the valve flow passage to generally prevent refrigerant flow therethrough such that the first restriction controls refrigerant flow through the refrigerant passageway and a second position opening the valve flow passage to permit refrigerant flow therethrough such that the second restriction controls refrigerant flow through the refrigerant passageway. The device further includes a biasing member within the body and resiliently urging the poppet into the first position. The poppet is movable from the first position to the second position in response to fluid pressure acting on the poppet to relieve high pressure spikes.
According to another aspect of the present invention, the present invention provides a refrigeration system. The refrigeration system has a compressor, a condenser, and an evaporator connected in series, and an expansion device located between the condenser and the evaporator. The refrigeration system includes an expansion device body having an inlet and an outlet and forming a refrigerant passageway extending from the inlet to said outlet and a poppet within said body. The refrigerant passageway having a valve flow passage and first and second restrictions. The poppet is movable between a first position closing the valve flow passage to generally prevent refrigerant flow therethrough such that the first restriction controls refrigerant flow through the refrigerant passageway and a second position opening the valve flow passage to permit refrigerant flow therethrough such that the second restriction controls refrigerant flow through the refrigerant passageway. The device further includes a biasing member within the body and resiliently urging the poppet into the first position. The poppet is movable from the first position to the second position in response to fluid pressure acting on the poppet to relieve high pressure spikes.
According to yet another aspect of the present invention, the present invention provides a method of delivering refrigerant from a high pressure region to a low pressure region of a refrigeration system to expand the refrigerant as it enters the low pressure region. The method includes the step of coupling the high and low pressure regions through a body having an inlet and an outlet and forming a refrigerant passageway extending from the inlet to the outlet. The passageway has a valve flow passage and first and second restrictions. A poppet is mounted within the valve body such that the poppet is movable between a first position closing the valve flow passage to generally prevent refrigerant flow therethrough wherein the first restriction controls refrigerant flow through the refrigerant passageway and a second position opening the valve flow passage to permit refrigerant flow therethrough wherein the second restriction controls refrigerant flow through the refrigerant passageway. The poppet is biased into the first position. The poppet is automatically moved to the second position in response to a predetermined fluid pressure acting on the poppet to relieve high pressure spikes.